T3 L3: Formation of urine

Question 1

What is the normal GFR?

Answer 1

125 mL/min

Question 2

What is ultrafiltration?

Answer 2

Filtration on a molecular scale

Question 3

What are the 3 layers that filtrate has to pass through during glomerular filtration?

Answer 3

1. Pores in the glomerular capillary endothelium
2. Basement membrane of Bowmans capsule
3. Epithelial cells of Bowmans capsule (the podocytes)

Question 4

What is the function of Mesangial cells and where are they found?

Answer 4

They contract and relax to allow molecules to go through the basement membrane of the Bowmans capsule

Question 5

What is the function of Podocytes and where are they found?

Answer 5

They cover glomerular capillaries and have pedicels that interconnect but leave small gaps so that molecules can get through

Question 6

How does diabetes damage podocytes?

Answer 6

Podocytes are very sensitive and high [glucose] is toxic to them so with diabetes, they die, break off and end up in urine which leaves gaps in the glomerular membrane

Question 7

What is oncotic pressure?

Answer 7

Pressure induced by proteins

Question 8

What are the 3 pressures that affect glomerular filtration?

Answer 8

1. Pressure within the glomerular capillary
2. Plasma protein pressure
3. Pressure within the Bowmans capsule

Question 9

How does the GFR remain constant even when systemic blood pressure changes?

Answer 9

Because of autoregulation of the renal blood flow. This process is not regulated by hormones or neurones

Question 10

What are the 2 hypotheses behind autoregulation of renal blood flow?

Answer 10

1. Myogenic. In response to the renal arterioles stretching
2. Metabolic. Renal metabolites modulate afferent and efferent arteriole contraction and dilation

But it’s believed that the process needs both

Question 11

What is the macula densa?

Answer 11

The part that detects the changes in Na+ and has an effect on blood pressure

Question 12

How can changes in GFR alter systemic blood pressure?

Answer 12

1. A drop in filtration pressure causes a drop in GFR
2. Lower GFR means less Na+ enters the proximal tubule
3. Tubular Na+ changes are detected by the macula densa
4. Juxtaglomerular cells will release renin in response to this
5. Renin causes formation of angiotensin II
6. Angiotensin II is a vasoconstrictor that causes BP to increase
7. Increased BP causes filtration pressure to increase and the GFR goes back to normal

Question 13

What do -pril drugs do?

Answer 13

They’re ACE inhibitors

Question 14

What do -sartan drugs do?

Answer 14

They’re angiotensin receptor blockers (ARB’s)

Question 15

What do -kiren drugs do?

Answer 15

They inhibit renin

Question 16

What does the Na+/K+ ATPase do?

Answer 16

It pumps Na+ against the chemical gradient into the peritubular capillary (3 Na+ leave, 2 K+ enter)

Question 17

Which ion follows Na+ to always balance out the charges?

Answer 17

Cl- by facilitated diffusion, and water

Question 18

Why do proximal tubule (PT) cells have a low intracellular [Na+]?

Answer 18

Because the Na+/K+ ATPase pumps all the Na+ out in return for K+

Question 19

What % of water is reabsorbed in the proximal tubule (PT)?

Answer 19

60-70%, active transport of Na+ out of PT cells is the driving force

Question 20

What structures allow for transcellular water absorption and where are they found?

Answer 20

Aquaporin channels found on the apical and basolateral surfaces

Question 21

Is there any active water reabsorption in the nephron?

Answer 21

None. It all occurs by osmosis and it follow Na+

Question 22

How many types of aquaporins (AQP) are found in the kidneys?

Answer 22

4

Question 23

Where are AQP1 found?

Answer 23

On the proximal tubule and other parts where water is reabsorbed. They are found on the apical membranes

Question 24

Where are AQP2 found?

Answer 24

On the collecting ducts on apical surfaces

Question 25

Expression of which AQP is controlled by ADH?

Answer 25

AQP2

Question 26

Where are AQP3/4 found?

Answer 26

On the basolateral surface of tubular cells involved in water reabsorption

Question 27

Where is glucose reabsorbed in the nephron?

Answer 27

The proximal tubule

Question 28

How is glucose transported in the nephron?

Answer 28

It’s co-transported into the proximal tubule cell with Na+

Question 29

What is the difference between SGLT1 and SGLT2?

Answer 29

SGLT2 has a lower affinity but higher capacity and transports 90% of the glucose. SGLT1 has a higher affinity but low capacity and only transports 10% of glucose

Question 30

What is a SGLT?

Answer 30

A sodium-glucose transporter

Question 31

What happens to SGLT when there is too much glucose?

Answer 31

They can’t handle it so some glucose will be excreted

Question 32

What do -flozin drugs do?

Answer 32

They are taken by type 2 diabetics to block SGLT2 so more glucose can be excreted and therefore blood glucose will be reduced. It can be used as a weight loss drug is hypoglycaemia is dangerous

Question 33

What % of K+ is reabsorbed by the PT?

Answer 33

70%

Question 34

What % of urea is reabsorbed by the PT?

Answer 34

40-50%

Question 35

What process reabsorbs proteins into to PT?

Answer 35

Receptor-mediated endocytosis

Question 36

Describe the process of protein reabsorption in the PT

Answer 36

Proteins are reabsorbed by pinocytosis, vesicles are transported into the cell, degraded by lysosomes and amino acids are then returned into the blood

Question 37

What is pinocytosis?

Answer 37

Ingestion into a cell by budding of vesicles from the membrane